1. Field of Use
This invention relates generally to apparatus for controlling the condensate level in steam retorts, such as canned food cookers or the like.
More specifically, the invention relates to improved electric control means and condensate level sensing means employed therein for operating condensate drain valves and other equipment used in such apparatus.
2. Description of the Prior Art
Steam retorts or steam cookers, which take various forms, are used in the food processing industry to heat and thereby sterilize and/or cook food contained in sealed metal cans. One type of steam retort or cooker takes the form of a large vessel having a sealable chamber in which cans containing the product to be heated are disposed. A cooker on the order of 8 feet high and 6 feet in diameter can hold about 5800 cans of the #303 size (about 16 ounces). Means are provided for continuously injecting high-pressure steam into the chamber at a temperature and for a period of time necessary to completely sterilize and/or cook the product. Steam at pressures up to 20 pounds per square inch and at temperatures up to 350.degree. F. may be injected for periods ranging from 25 minutes to about 4 hours. A condensate well is provided at the bottom of the chamber below the cans to collect the condensate formed as the steam cools after mingling with and heating the cans. For reasons of thermal efficiency and fuel economy, waste space between the level of the condensate and the lowermost layer of cans in the chamber is kept at a minimum. If, for example, the incoming steam is at a temperature of 250.degree. F. (the minimum sterilizing temperature for all products) and sufficient to heat the product being processed, then the temperature of the condensate could be low as 227.degree. F. However, if such low-temperature condensate being collected in the well were to rise and reach the cans, the product in some cans would cool and fail to reach and/or remain at the proper elevated temperature. Improper sterilization creates a risk of product spoilage and the further risks of botulism and loss of product. Accordingly, it is the practice (and required by federal regulations, as explained below) to provide a suitable drain in the condensate well to remove the condensate before its level rises too high and the risk of spoilage can occur. It should be noted that excessive condensate build-up can be caused by relatively low temperature of the product when introduced into the retort chamber, or by can size and length of cooking time required, or by the temperature in the cooking room or any combination thereof. In addition, condensate level variations most often occur during extended cooking and cooling periods common to batch operations, and may not leave a water line sufficient to determine visually what the condensate level is or was.
Because of the health risk, current U. S. Government federal regulations provide:
"The condensate bleeder shall be checked with sufficient frequency to ensure adequate removal of condensate or shall be equipped with an automatic alarm system(s) that would serve as a continuous monitor of condensate-bleeder functioning. Visual checks should be done at intervals of not more than 15 minutes. A record of such checks should be kept to show that the bleeder is functioning properly.
At the time steam is turned on, the drain should be opened for a time sufficient to remove steam condensate from the retort, and provision shall be made for continuing drainage of condensate during the retort operation. The condensate bleeder in the bottom of the shell serves as an indicator of continuous condensate removal."
In compliance with these regulations, it is common practice to visually inspect the condensate build-up regularly or rely on warning devices to determine when the drain should be opened, or to construct the cooker or retort so that steam is continuously blown from a drain which is always open, thus insuring that no condensate build-up occurs. Suitable records are also kept of condensate levels and drain operation. These monitoring procedures are time-consuming and costly. The continuous exhausing of steam to atmosphere is wasteful of energy and extremely costly.
Prior art efforts to monitor condensate levels in steam retorts or cookers and to take appropriate steps with respect thereto, as by initiating drainage and/or recording conditions, have not met with commercial success. In particular, because of the relatively high temperature and pressures encountered in steam cookers or retorts, as well as the presence of moisture, and because of the wide fluctuation of the liquid levels to be sensed and regulated, prior art control systems and liquid level sensing components which are presently available commercially are not well-suited to such an environment.
For example, U.S. Pat. No. 3,357,247, issued Dec. 12, 1967 to Charles Robert Bardes et al, discloses the use of a liquid level sensing device to visually indicate the presence of liquid condensate in a drum pressurized by steam. The following three patents disclose use of float valves to indicate fluid levels: U.S. Pat. Nos. 2,846,985, issued Aug. 12, 1958 to A. G. Blanchard; 3,675,614, issued July 11, 1972 to John T. Ward et al.; 2,709,919, issued June 7, 1955 to G. B. Huttenlock et al. U.S. Pat. No. 3,078,918, issued Feb. 26, 1963 to W. H. Magearl et al. shows use of a float-driven system with appropriate controls and alarms.